Abstract
Finite element analysis (FEA) for creep life assessment of large-scale structures is challenging due to the highly nonlinear (iterative) nature of creep analysis, the long timescales involved, and the substantial number of FEA degrees of freedom to consider strong interaction between components in full scale system. One of the methods explored to overcome the challenges was the linear-nonlinear hybrid formulation which significantly reduces analysis time with reasonably acceptable accuracy.
The approach used in the analysis takes advantage of the fact that, in practice, we are usually interested in a specific region of a system where creep develops faster than the other regions, and thus we can treat that local region as a locally nonlinear problem that will be analyzed using nonlinear finite element analysis (FEA) while the other regions will be analyzed using Reduced Basis Finite Element Analysis (RB-FEA). The FEA and RB-FEA regions are fully coupled via the Hybrid Solver approach, yielding an accurate solution for the overall nonlinear system. The accuracy of the solution over the entire model is maintained by employing appropriate component training processes to infer the behavior of the field over the entire model, including the linear-nonlinear interface.
The paper presents the creep analysis results for simple Tee joint, multiple Tee joints in a piping, and more complicated piping system consisting of main header, sub-header, and smallbore piping, and demonstrates validity and effectiveness of the proposed method by comparing stress relaxation, cumulative creep strain, solving time and memory consumption to standard FEA.
